[Problems] To provide a bath for surface treatment capable of forming a surface-treating film having excellent corrosion resistance by a high-speed electrolytic treatment, and a method of producing a surface-treated steel plate having excellent corrosion resistance and closely adhering property to the coating maintaining good productivity. [Means for Solution] A bath for surface treatment used for forming a surface-treating film on the surface of a steel plate by cathodic electrolysis, the bath for surface treatment containing Zr and/or Ti, and a polycarboxylic acid. [Selected Drawing] None